Successful Local Anesthesia: What Endodontists Need to Know

Patients in pain will be hard to anesthetize for a number of reasons (for example, TTX receptors, decreased excitability thresholds, altered resting potentials, excitability of nociceptors isoforms, and patient apprehension) (1). Currently, there is no simple solution to anesthetizing mandibular molars in patients presenting with symptomatic irreversible pulpitis. That is, there is no magic solution or technique for nerve block that will provide predictable pulpal anesthesia (1). In the majority of patients, only supplemental techniques will be effective (1).

Symptomatic Irreversible Pulpitis

Mandibular Success (no or mild pain upon endodontic access or instrumentation) of the inferior alveolar nerve block (IANB)(2) in these patients will be around 28% for the first molars, 25% for the second molars, and 39% for the premolars - which will not be high enough to ensure profound pulpal anesthesia. Additionally, articaine is not better than lidocaine for IANBs (1). Mepivacaine plain (3% Carbocaine, 3% Polocaine) is the same as 2% lidocaine with 1:100,000 epinephrine for IANBs (1). This is very important clinically because the plain 3% mepivacaine could be used in patients when epinephrine is contraindicated or medical conditions dictate caution.

One important fact to remember: Patients do not always achieve pulpal anesthesia with the IANB in endodontics (1), but this is NOT your fault.

What Methods may Increase Success in Patients?

Oral Conscious Sedation

Triazolam (Halcion)(1) and alprazolam (Xanax)(3) should not be used as a way to reduce pain during endodontic treatment because consciously-sedated patients will be able to detect and experience pain unless measures are used to provide profound local anesthesia; they can be used for anxiety reduction.

Gow-Gates Technique

Using a two-cartridge volume of 2% lidocaine with 1:100,000 epinephrine, the success rate with the Gow-Gates technique of 35% (4) was similar to the 24% to 35% success rates of the IANB in previous studies in patients presenting with symptomatic irreversible pulpitis (1).

Buffered Anesthetic Solutions

A 2% or 4% buffered lidocaine formulation (with epinephrine) did not result in an increase in the success rate, or a decrease in injection pain, over non-buffered lidocaine formulations with epinephrine in patients presenting with symptomatic irreversible pulpitis (5, 6). Theoretically, the higher pH should have resulted in a higher success rate. However, the body intrinsically has an efficient buffering system that maintains tissues at physiologic pH. The pH conversion buffering process could occur within several minutes. One study reported a freshly prepared 2% lignocaine with epinephrine formulation (pH 5.25) being converted to a pH of 7.17 within three minutes following an intradermal injection (7). This physiologic conversion may help explain why buffering an anesthetic did not demonstrate any benefit in increasing anesthetic success.

Supplemental Buccal Infiltration of Articaine

In patients with symptomatic irreversible pulpitis, a supplemental buccal infiltration of articaine is not reliable for pulpal anesthesia. Success rates (ability to access and instrument the tooth without pain or mild pain) were only 42% for the first molars, 48% for the second molars, and 73% for the premolars (2).

Effect of Preemptive Medications on Success

Ibuprofen, a combination of ibuprofen/acetaminophen, and a combination of acetaminophen/hydrocodone (1, 8) have been given preemptively before the IANB. No significant effect was shown on the success of the IANB. Other preemptive medications (ketorolac, indomethacin, diclofenac, and others) have shown mixed results (9-11). Further analysis on the use of these other preemptive medications should be performed in patients presenting with symptomatic irreversible pulpitis.

Proven Supplemental Methods to Help with Pulpal Anesthesia in Symptomatic Irreversible Pulpitis

Intraosseous Anesthesia

The supplemental intraosseous injection, using the Stabident or X-tip system, of a cartridge of 2% lidocaine with 1:100,000 epinephrine will be successful approximately 90% of the time in mandibular posterior teeth (1, 12-14). Onset is immediate and duration is very good for the endodontic appointment. The supplemental intraosseous injection of a cartridge of mepivacaine plain (3% Carbocaine, 3% Polocaine) will be successful 80% of the time (1). Repeating the intraosseous injection using another cartridge of 3% mepivacaine will increase success to 98%1. This plain solution could be used in patients when epinephrine is contraindicated or when medical conditions dictate caution.

Intraligamentary (PDL) Injection

A supplemental intraligamentary injection is successful from 48% to 74% of the time (1, 12, 15). Re-injection will increase success to over 90%. However, duration of pulpal anesthesia is fairly short.

Nitrous Oxide

Nitrous oxide has a potential benefit because of its sedation and analgesic effects. Administration of 30%-50% nitrous oxide will increase the success of the IANB in patients with irreversible pulpitis16. When supplemental intraosseous or intraligamentary injections fail and the pulp is not exposed, administering nitrous oxide is very helpful in achieving anesthesia.

Intrapulpal Anesthesia

In approximately 5-10% of patients with irreversible pulpitis, supplemental injections do not produce pulpal anesthesia. Therefore, intrapulpal anesthesia is indicated and will be successful if given under backpressure. The disadvantage is that the injection is painful and should only be used after all other supplemental techniques have been given.

The success (no or mild pain upon endodontic access or instrumentation) ranged from 54% to 88%1, 17 using a one or two-cartridge volume of 2% lidocaine with 1:100,000 epinephrine. Therefore, not all patients achieve pulpal anesthesia. There doesn't appear to be a difference between articaine and lidocaine for maxillary buccal infiltrations18-20. It has also been found that longer roots may be associated with more failures21.

Incision and Drainage Procedure

Buffering lidocaine did not significantly decrease the pain of infiltrations before I & D or significantly decrease the pain of the I & D procedure, when compared to a non-buffered 2% or 4% lidocaine (with epinephrine) formulation, in symptomatic patients presenting with moderate-to-severe pain, a diagnosis of pulpal necrosis and an associated acute swelling22, 23. Additionally, moderate-to-severe pain was experienced in a large number of patients with the I & D procedure. While the theory of buffering local anesthetics is logical, in reality the presence of a buffer in the local anesthetic may not be enough to overcome the lowered excitability thresholds and peripheral sensitization associated with such significant inflammatory and infectious conditions in a patient with pulpal necrosis and associated acute swelling.

New Formulations for Anesthesia

Kovanaze Nasal Spray

The combination of tetracaine topical anesthetic and oxymetazoline (a vasoconstrictor) has recently been approved by the FDA for dental use. It could be used in patients who are needle phobic and has been recommended for restorative procedures on teeth numbers 4 to 13 and A to J (in children who weigh 88 pounds or more). Further research is needed to confirm the efficacy of the Kovanase nasal spray for anesthesia of maxillary teeth and for endodontic patients.

Exparel (Liposomal Bupivacaine)

Administration of Exparel (theoretically providing local anesthesia for up to 72 hours because of the slow release of bupivacaine) as an infiltration (it is not approved for nerve blocks) did not reduce pain to manageable clinical levels in patients with untreated, symptomatic irreversible pulpitis (24) or postoperatively following debridement in symptomatic patients, diagnosed with pulpal necrosis, and experiencing moderate to severe preoperative pain (25). Perhaps, in the future, Exparel could be studied for nerve blocks following FDA approval.

We have made significant advances in pain management for our endodontic patients. The future may hold even more exciting developments.

Dr. Reader currently serves as professor emeritus and program director of advanced endodontics at Ohio State University in Columbus, Ohio. He was also a director of the American Board of Endodontics. He has authored over 100 papers and abstracts, and presented over 80 lectures to societies and professional organizations. His research includes local anesthesia and endodontics. He received his D.D.S. and M.S. degrees and endodontic training from OSU.